Catalytic reforming process to produce high octane gasoline

ABSTRACT

The present invention is a multistage reforming process to produce high octane product from naphtha boiling range feed. In the process, a effluent product from a penultimate reforming stage is separated into at least a first stream and a second stream by boiling point. The lower boiling of the two streams is further reformed in a final reforming stage over a medium pore molecular sieve catalyst.

FIELD OF THE INVENTION

The present invention relates to a multistage reforming process using a medium pore molecular sieve catalyst to produce a high octane naphtha at high liquid yield and hydrogen production.

BACKGROUND OF THE INVENTION

Catalytic reforming is one of the basic petroleum refining processes for upgrading light hydrocarbon feedstocks, frequently referred to as naphtha feedstocks. Products from catalytic reforming can include high octane gasoline useful as automobile fuel, aromatics (for example benzene, toluene, xylenes and ethylbenzene), and/or hydrogen. Reactions typically involved in catalytic reforming include dehydrocylization, isomerization and dehydrogenation of naphtha range hydrocarbons, with dehydrocyclization and dehydrogenation of linear and slightly branched alkanes and dehydrogenation of cycloparaffins leading to the production of aromatics. Dealkylation and hydrocracking are generally undesirable due to the low value of the resulting light hydrocarbon products.

Catalysts commonly used in commercial reforming reactions often include a Group VIII metal, such as platinum or palladium, or a Group VIII metal plus a second catalytic metal, which acts as a promoter. Examples of metals useful as promoters include rhenium, tin, tungsten, germanium, cobalt, nickel, rhodium, ruthenium, iridium or combinations thereof. The catalytic metal or metals may be dispersed on a support such as alumina, silica, or silica-alumina. Typically, a halogen such as chlorine is incorporated on the support to add acid functionality. In addition to Group VIII metals, other reforming catalysts include aluminosilicate zeolite catalysts. For example, U.S. Pat. Nos. 3,761,389, 3,756,942 and 3,760,024 teach aromatization of a hydrocarbon fraction with a ZSM-5 type zeolite catalyst. U.S. Pat. No. 4,927,525 discloses catalytic reforming processes with beta zeolite catalysis containing a noble metal and an alkali metal. Other reforming catalysts include other molecular sieves such as bore-silicates and silicoaluminophosphates, layered crystalline clay-type phyllosilicates, and amorphous clays.

In addition to selection of catalysts for reforming, various processes for reforming a naphtha feedstock in one or more process steps to produce higher value reformate products are known in the art. U.S. Pat. No. 3,415,737 teaches a process for reforming naphtha under conventional mild reforming conditions with a platinum-rhenium-chloride reforming catalyst to increase the aromatics content and octane number of the naphtha. In U.S. Pat. No. 3,770,614 there is disclosed a process in which a reformate is fractionated and the light reformate fraction (C6 fraction) passed over a ZSM-5-type zeolite to increase aromatic content of the product. U.S. Pat. No. 3,950,241 discloses a process for upgrading naphtha by separating it into low- and high-boiling fractions, reforming the low-boiling fraction, combining the high-boiling naphtha with the reformate, and contacting the combined fractions with a ZSM-5-type catalyst. U.S. Pat. No. 4,181,599 discloses a process for reforming naphtha comprising separating the naphtha into heavy and light fractions and reforming and isomerizing the naphtha fractions. U.S. Pat. No. 4,190,519 teaches a process for upgrading a naphtha-boiling-range hydrocarbon which comprises separating the naphtha feedstock into a light naphtha fraction containing C6 paraffins and lower-boiling hydrocarbons and a heavy naphtha fraction containing higher-boiling hydrocarbons, reforming the heavy naphtha fraction and passing at least a portion of the reformate together with the light naphtha fraction over a zeolite catalyst to produce an aromatics-enriched effluent. Different catalysts may be employed in different process steps during the reforming of naphtha feedstocks as described in U.S. Pat. No. 4,627,909, U.S. Pat. No. 4,443,326, U.S. Pat. No. 4,764,267, U.S. Pat. No. 5,073,250, U.S. Pat. No. 5,169,813, U.S. Pat. No. 5,171,691, U.S. Pat. No. 5,182,012, U.S. Pat. No. 5,358,631, U.S. Pat. No. 5,376,259 and U.S. Pat. No. 5,407,558, for example.

Even with the advances in naphtha reforming catalysts and processes, a need still exists to develop new and improved reforming methods to provide higher liquid yield, improve hydrogen production, and minimize the formation of less valuable low molecule weight (C₁-C₄) products. It has been discovered that interstage feed separation in a staged reforming process and lower pressure in the final stage of a multistage reforming process can improve the RON (Research Octane Number), aromatics content, C₅+ liquid yield, hydrogen production, and catalyst life.

SUMMARY OF THE INVENTION

The present invention relates to processes for catalytically reforming a naphtha fuel feed to produce a product reformate in a multistage reforming operation. The process comprises contacting a naphtha boiling range hydrocarbon feedstock in a penultimate stage of a multi-stage reforming process at a first reforming pressure to produce a penultimate effluent; separating at least a portion of the penultimate effluent into at least an intermediate reformate and a heavy reformate, wherein the intermediate reformate has a mid-boiling point that is lower than that of the heavy reformate; and contacting the intermediate reformate in a final stage of the multi-stage reforming process at a second reforming pressure with a catalyst comprising at least one medium pore molecular sieve to produce a final effluent comprising a final reformate, wherein the first reforming pressure is greater than the second reforming pressure.

In embodiments, the catalyst within the penultimate stage comprises a Group VIII metal and a promoter supported on a porous refractory inorganic oxide support. In embodiments, the catalyst within the final stage comprises a Group VIII metal.

In another embodiment, a reforming process comprises contacting a naphtha boiling range hydrocarbon feedstock in a penultimate stage of a multi-stage reforming process at a first reforming pressure to produce a penultimate effluent; separating at least a portion of the penultimate effluent into at least a light reformate, an intermediate reformate and a heavy reformate, wherein the light reformate has a mid-boiling point that is lower than that of the intermediate reformate, and wherein the intermediate reformate has a mid-boiling point that is lower than that of the heavy reformate; and contacting the intermediate reformate in a final stage of the multi-stage reforming process at a second reforming pressure with a catalyst comprising at least one medium pore molecular sieve to produce a final effluent comprising a final reformate, wherein the first reforming pressure is greater than the second reforming pressure.

Other aspects, features and advantages will be apparent from the description of the embodiments thereof and from the claims.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a schematic diagram of one embodiment of the invention.

FIG. 2 is a schematic diagram of a second embodiment of the invention.

DETAILED DESCRIPTION

In the present process, a naphtha boiling range hydrocarbon feedstock is processed in a multi-Stage reforming process, which process involves at least a penultimate stage for reforming the naphtha feedstock to a penultimate stage naphtha product which has an octane number higher than that of the naphtha feed and a final stage for further reforming a portion of an effluent product from the penultimate stage, producing a final naphtha having an octane number higher than that of the penultimate stage naphtha product. The reforming process is operated at conditions and with catalysts selected for conducting dehydrocyclization, isomerization and dehydrogenation reactions for converting low octane normal paraffins and cycloparaffins into high octane materials. In this way, a product having increased octane and/or containing an increased amount of aromatics is produced. In some embodiments, the multi-stage reforming process is operated at conditions and with one more catalysts for producing a net positive quantity of hydrogen.

The multi-stage reforming process comprises passing a refinery stream through at least two reforming stages in series. In general, each reforming stage is characterized by one or more reforming reactor vessels, each containing a catalyst and maintained at reforming reaction conditions. The product from each stage before the final stage is passed, in whole or in part, to the succeeding stage in the multi-stage process. The temperature of the product from each stage which is passed to a succeeding stage may be increased or decreased to meet the particular needs of the process. Likewise, the pressure of the product which is passed to a succeeding stage before the final stage may be increased or decreased, with the proviso that the pressure in the penultimate stage is higher than the pressure in the final stage.

While the discussion which follows relates at times, for convenience, to operation of penultimate and final reforming stages, the principles of the invention are applicable as between any two successive stages and can be applied to several sequentially connected stages. In essence then, the term final stage as used herein does not necessarily indicate the last stage if there are three or more stages, but father indicates a succeeding stage which follows a preceding (often referred to for convenience as “penultimate”) stage.

DEFINITIONS

As disclosed herein, boiling point temperatures are based on ASTM D-2887 standard test method for boiling range distribution of petroleum fractions by gas chromatography, unless otherwise indicated. The mid-boiling point is defined as the 50% by volume boiling temperature, based on an ASTM D-2887 simulated distillation.

As disclosed herein, carbon number values (i.e. C₅, C₆, C₈, C₉ and the like) of hydrocarbons may be determined by standard gas chromatography methods. Unless otherwise specified, Research Octane Number (RON) is determined using the method described in ASTM D2699.

Unless otherwise specified, feed rate to a catalytic reaction zone is reported as the volume of feed per volume of catalyst per hour. In effect, the feed rate as disclosed herein, referred to as liquid hourly space velocity (LHSV), is reported in reciprocal hours (i.e. hr⁻¹).

As used herein, a C₁− stream comprises a high proportion of hydrocarbons with 4 or fewer carbon atoms per molecule. Likewise, a C₅+ stream comprises a high proportion of hydrocarbons with 5 or more carbon atoms per molecule. It will be recognized by those of skill in the art that hydrocarbon streams in refinery processes are generally separated by boiling range using a distillation process. As such, the C₄− stream would be expected to contain a small quantity of C₅, C₆ and even C₇ molecules. However, a typical distillation would be designed and operated such that at least about 70% by volume of a C₄− stream would contain molecules having 4 carbon atoms or fewer per molecule. As used herein, C₅+, C₆-C₈, C₉+ and other hydrocarbon fractions identified by carbon number ranges would be interpreted likewise.

The term “silica to alumina ratio” refers to the molar ratio of silicon oxide (SiO₂) to aluminum oxide (Al₂O₃).

As used herein the term “molecular sieve” refers to a crystalline material containing pores, cavities, or interstitial spaces of a uniform size in which molecules small enough to pass through the pores, cavities, or interstitial spaces are adsorbed while larger molecules are not. Examples of molecular sieves include zeolites and non-zeolitic molecular sieves such as zeolite analogs including, but not limited to, SAPOs (silicoaluminophosphates), MeAPOs (metalloaluminophosphates), AlPO₄, and ELAPOs (nonmetal substituted aluminophosphate families).

When used in this disclosure, the Periodic Table of the Elements referred to is the CAS version published by the Chemical Abstract Service in the Handbook of Chemistry and Physics, 72^(nd) edition (1991-1992).

Among other factors, the present invention is based on the discovery that selective reforming of paraffins, especially C₆-C₈ paraffins, in a separate or additional reforming stage provides improved performance of the overall reforming process. Thus, a penultimate reforming stage using a conventional reforming catalyst is operated at relatively low severity, since it is not required to reach the high octane levels normally desired for a naphtha fuel or fuel blend stock. Under these conditions the catalyst catalyzes the more facile reactions, such as cyclohexane and alkycyclohexane dehydrogenation, while keeping hydrocracking to a minimum. Generally, a conventional catalyst used to dehydrocyclize paraffins under more severe conditions produces higher quantities of light gases, on account of the catalyst being somewhat unselective for dehydrocyclization. With the present invention, however, an intermediate reformate from a penultimate reforming stage is passed to a final reforming stage containing a medium pore molecular sieve catalyst. The performance characteristics of the medium pore molecular sieve catalyst permits operating a final stage in the multi-stage reforming process at a reduced pressure, which increases the selectivity of C₆-C₈ paraffin dehydrocyclization while maintaining low catalyst fouling rates. The C₉+ fraction from the penultimate stage has higher octane than the C₆-C₈ intermediate fraction, and is not further reformed in the final stage. Otherwise, the high octane C₉+ fraction from the penultimate stage will undergo some cracking and/or dealkylation reactions in the final stage, which lowers the liquid yield and consumes hydrogen. Consequently, the performance characteristics of the catalyst of the final stage provide complementary benefits, resulting in an overall process which produces a high octane product at ah improved liquid yield and hydrogen production.

The naphtha boiling range feedstock entering the penultimate stage of the multi-stage process is a naphtha fraction boiling within the range from about of 50° to about 550° F. and preferably from 70° to 450° F. In embodiments, the reformer feed is a C₅+ feed. The reformer feed can include, for example, straight run naphthas, paraffinic raffinates from aromatic extraction or adsorption, and C₆-C₁₀ paraffin-rich feeds, bioderived naphtha, naphtha from hydrocarbon synthesis processes, including Fischer Tropsch and methanol synthesis processes, as well as naphtha products from other refinery processes, such as hydrocracking or conventional reforming. In reforming processes involving more than two stages, the reformer feed may comprise at least a portion of the product generated in a preceding stage.

The reforming catalyst used in the penultimate reforming stage may be any catalyst known to have catalytic reforming activity. In embodiments, the penultimate stage catalyst comprises a Group VIII metal disposed on an oxide support. Example Group VIII metals include platinum and palladium. The catalyst may further comprise a promoter, such as rhenium, tin, germanium, cobalt, nickel, iridium, tungsten, rhodium, ruthenium, or combinations thereof. In some such embodiments, the promoter metal is rhenium or tin. These metals are disposed on a support, such as alumina, silica/alumina, or silica. In some such embodiments, the support is alumina. The support may also include natural or man-made zeolites. The catalyst may also include between 0.1 and 3 weight percent chloride, preferably between 0.5 and 1.5 weight percent chloride. The catalyst, if it includes a promoter metal, suitably includes sufficient promoter metal to provide a promoter to platinum ratio between 0.5:1 and 10:1 or between 1:1 and 6:1. The precise conditions, compounds, and procedures for catalyst manufacture are known to those persons skilled in the art. Some examples of conventional catalysts are shown in U.S. Pat. Nos. 3,631,216; 3,415,737; and 4,511,746, which are hereby incorporated by reference in their entireties.

The catalysts in both the penultimate stage and the final stage may be employed in the form of pills, pellets, granules, broken fragments, or various special shapes, disposed as a fixed bed within a reaction zone, and the charging stock may be passed therethrough in the liquid, vapor, or mixed phase, and in either upward, downward or radial flow. Alternatively, they can be used in moving beds or in fluidized-solid processes, in which the charging stock is passed upward through a turbulent bed of finely divided catalyst. However, a fixed bed system or a dense-phase moving bed system are preferred due to the lower catalyst attrition losses and other operational advantages. In a fixed bed system, the feed is preheated (by any suitable heating means) to the desired reaction temperature and then passed into a reaction zone containing a fixed bed of the catalyst. This reaction zone may be one or more separate reactors with suitable means to maintain the desired temperature at the reactor entrance. The temperature must be maintained because reforming reactions are typically endothermic in nature.

The actual reforming conditions in both the penultimate and the final reforming stages will depend, at least in part, on the feed used, whether highly aromatic, paraffinic or naphthenic and upon the desired octane rating of the product and desired hydrogen production.

The penultimate stage is maintained at relatively mild reaction conditions, so as to inhibit the cracking of the stream being upgraded, and to increase the useful lifetime of the catalyst in the penultimate stage. The naphtha boiling range feedstock to be upgraded in the penultimate stage contacts the penultimate stage catalyst at reaction conditions, which conditions include a temperature in the range from about 800° F. to about 1100° F., a pressure in the range from greater than 70 psig to about 400 psig, and a feed rate in the range of from about 0.5 hr⁻¹ to about 5 hr⁻¹ LHSV. In some embodiments, the pressure in the penultimate stage is in the range from about 200 psig to about 400 psig.

The effluent from the penultimate stage is an upgraded product, in that the RON has been increased during reaction in the penultimate stage. The penultimate stage effluent comprises hydrocarbons and hydrogen generated during reaction in the penultimate stage and at least some of the hydrogen, if any, which is added to the feed upstream of the penultimate stage. The effluent hydrocarbons may be characterized as a mixture of C₄− hydrocarbons and C₅+ hydrocarbons, the distinction relating to the molecular weight of the hydrocarbons in each group. In embodiments, the C₅+ hydrocarbons in the effluent have a combined RON of at least 85.

The effluent from the penultimate stage (otherwise termed the “penultimate-effluent”) comprises C₅+ hydrocarbons which are separated into at least an intermediate reformate and a heavy reformate. The effluent further comprises hydrogen and C₄− hydrocarbons. A hydrogen-rich stream may separate from the effluent in a preliminary separation step, using, for example, a high pressure separator or other flash zone. C₄− hydrocarbons in the effluent may also be separated in a preliminary separation, either along with the hydrogen or in a subsequent flash zone. The intermediate reformate is characterized as having a lower mid-boiling point than that of the heavy reformate. In some embodiments, the intermediate reformate boils in the range from about 70° F. to about 280° F. In some such embodiments, the intermediate reformate comprises at least 70 vol % C₅-C₉ hydrocarbons. In some embodiments, the intermediate reformate boils in the range from about 100° F. to about 280° F. In some such embodiments, the intermediate reformate comprises at least 70 vol % C₆-C₈ hydrocarbons. In some embodiments, the intermediate reformate boils in the range from about 100° F. to about 230° F. In some such embodiments, the intermediate reformate comprises at least 70 vol % C₆-C₇ hydrocarbons. Recovery of an intermediate reformate fraction may be accompanied by the further recovery of a largely C₅ light reformate fraction. The light reformate is characterized as having a lower mid-boiling point than that of the intermediate reformate. In some embodiments, the light reformate fraction boils in the range from about 70° F. to about 140° F. In some such embodiments, the light reformate fraction comprises at least 70 vol % C₅ hydrocarbons. The heavy reformate that is produced during separation of the upgraded product boils in the range of about 220° F. and higher. In some such embodiments, the heavy reformate comprises at least 70 vol % C₉+ hydrocarbons.

The RON of the intermediate reformate is indicative of the mild reforming conditions in the penultimate stage. As such, the intermediate reformate typically has an RON of greater than 65. In some embodiments the intermediate reformate has an RON within the range of about 65 to less than 100. In some such embodiments the intermediate reformate has an RON within the range of 65 to less than 95.

The final stage reforming catalyst comprises at least one medium pore molecular sieve. The molecular sieve is a porous inorganic oxide characterized by a crystalline structure which provides pores of a specified geometry, depending on the particular structure of each molecular sieve. The phrase “medium pore” as used herein means having a crystallographic free diameter in the range of from about 3.9 to about 7.1 Angstrom when the porous inorganic oxide is in the calcined form. The crystallographic free diameters of the channels of molecular sieves are published in the “Atlas of Zeolite Framework Types”, Fifth Revised Edition, 2001, by Ch. Baerlocher, W. M. Meier, and D. H. Olson, Elsevier, pp 10[ndash]15, which is incorporated herein by reference. Non-limiting examples of medium pore molecular sieves include ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48 MCM-22, SSZ-20, SSZ-25, SSZ-32, SSZ-35, SSZ-37, SSZ-44, SSZ-45, SSZ-47, SSZ-57, SSZ-58, SSZ-74, SUZ-4, EU-1, NU-85, NU-87, NU-88, IM-5, TNU-9, ESR-10, TNU-10 and combinations thereof. As used in this disclosure, the medium pore molecular sieve useful in the present process is a high silica ZSM-5 zeolite with a molar ratio of SiO₂/M₂O₃ of at least 40:1, preferably at least 200:1 and more preferably at least 500:1, where M is selected from Al, B, or Ga.

Various references disclosing ZSM-5 are provided in U.S. Pat. No. 4,401,555 to Miller. These references include the aforesaid U.S. Pat. No. 4,061,724 to Grose et al.; U.S. Pat. Reissue No. 29,948 to Dwyer et al.; Flanigan et al., Nature, 271, 512-516 (Feb. 9, 1978) which discusses the physical and adsorption characteristics of high silica ZSM-5. Anderson et al., J. Catalysis 58, 114-130 (1979) which discloses catalytic reactions and sorption measurements carried out on ZSM-5. The disclosures of these references, and U.S. Pat. No. 4,401,555, are incorporated herein by reference, particularly including their disclosures on methods of making high silica to alumina ZSM-5. Additional disclosure on the preparation and properties of high silica ZSM-5 may be found, for example, in U.S. Pat. No. 5,407,558 and U.S. Pat. No. 5,376,259.

In embodiments, the high silica ZSM-5 molecular sieve which is useful as a component of the catalyst in the present process has a molar silica to alumina molar ratio of at least 40:1, or at least 200:1, or at least 500:1. An example high silica molecular sieve has a silica to alumina molar ratio of at least 1000:1. In embodiments, the molecular sieve is characterized as having a crystallite size less than 10 μm, or less than 5 μm or less than 1 μm. Methods for determining crystallite size, using, for example Scanning Electron Microscopy, are well known. In embodiments, the high silica ZSM-5 is characterized as having at least 80% crystallinity, or at least 90% crystallinity, or at least 95% crystallinity. Methods for determining crystallinity, using, for example, X-ray Diffraction, are well known. Strong acidity is undesirable in the catalyst because it promotes cracking, resulting in lower selectivity to C₅+ liquid product. To reduce acidity, the molecular sieve preferably contains an alkali metal and/or an alkaline earth metal. The alkali or alkaline earth metals are preferably incorporated into the catalyst during or after synthesis of the molecular sieve. Preferably, at least 90% of the acid sites are neutralized by introduction of the metals, more preferably at least 95%, most preferably at least 99%. In one embodiment, the medium pore molecular sieve has less than 5,000 ppm alkali. Such medium pore silicate molecular sieves are disclosed, for example, in U.S. Pat. No. 4,061,724 and in U.S. Pat. No. 5,182,012. These patents are incorporated herein by reference, particularly with respect to the description, preparation and analysis of molecular sieves having the specified molar silica to alumina molar ratios, having a specified crystallite size, having a specified crystallinity and having a specified alkali content.

Other crystalline molecular sieves which can be used in the final reforming stage, include those as listed in U.S. Pat. No. 4,835,336, namely, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48, and other similar materials such as CZH-5 disclosed in Ser. No. 166,863 of Hickson, filed Jul. 7, 1980 and incorporated herein by reference.

SSZ-20 is disclosed in U.S. Pat. No. 4,483,835, and SSZ-23 is disclosed in U.S. Pat. No. 4,859,442, both of which are incorporated herein by reference.

ZSM-5 is more particularly described in U.S. Pat. No. 3,702,886 and U.S. Pat. Re. 29,948, the entire contents of which are incorporated herein by reference.

ZSM-11 is more particularly described in U.S. Pat. No. 3,709,979, the entire contents of which are incorporated herein by reference.

ZSM-12 is more particularly described in U.S. Pat. No. 3,832,449, the entire contents of which are incorporated herein by reference.

ZSM-22 is more particularly described in U.S. Pat. Nos. 4,481,177, 4,556,477 and European Pat. No. 102,716, the entire contents of each being expressly incorporated herein by reference.

ZSM-23 is more particularly described in U.S. Pat. No. 4,076,842, the entire contents of which are incorporated herein by reference.

ZSM-35 is more particularly described in U.S. Pat. No. 4,016,245, the entire contents of which are incorporated herein by reference.

ZSM-38 is more particularly described in U.S. Pat. No. 4,046,859, the entire contents of which are incorporated herein by reference.

ZSM-48 is more particularly described in U.S. Pat. No. 4,397,827 the entire contents of which are incorporated herein by reference.

The crystalline molecular sieve may be in the form of a borosilicate, where boron replaces at least a portion of the aluminum of the more typical aluminosilicate form of the molecular sieve. Borosilicate molecular sieves are described in U.S. Pat. Nos. 4,268,420; 4,269,813; 4,327,236 to Klotz, the disclosures of which patents are incorporated herein, particularly those disclosures related to borosilicate preparation.

Silicoaluminophosphates (SAPOs) are an example of nonzeolitic molecular sieves useful in the practice of the present invention. SAPOs comprise a molecular framework of corner-sharing [SiO₄] tetrahedra, [AlO₄] tetrahedra and [PO₄] tetrahedra linked by oxygen atoms. By varying the ratio of P/Al and Si/Al the acidity of the SAPO can be modified to minimize unwanted hydrocracking and maximize advantageous isomerization reactions. Preferred molar ratios of P/Al are from about 0.75 to 1.3 and preferred molar ratios of Si/Al are from about 0.08 to 0.5. Examples of a silcoaluminophosphate useful to the present invention include SAPO-11, SAPO-31, and SAPO-41, which are also disclosed in detail in U.S. Pat. No. 5,135,638.

The catalysts used in the final reforming stage according to the present invention contain one or more Group VIII metals, e.g., nickel, ruthenium, rhodium, palladium, iridium or platinum. The preferred Group VIII metals are iridium, palladium, and particularly platinum. They are more selective with regard to dehydrocyclization and are also more stable under the dehydrocyclization reaction conditions than other Group VIII metals. The preferred percentage of the Group VIII metals, such as platinum, in the catalyst is between 0.1 wt. % and 5 wt. %, more preferably from 0.3 wt. % to 2.5 wt. %. The catalyst may further comprise a promoter, such as rhenium, tin, germanium, cobalt, nickel, iridium, tungsten, rhodium, ruthenium, or combinations thereof.

In forming the final stage catalyst, the crystalline zeolite is preferably bound with a matrix. The matrix is not catalytically active for hydrocarbon cracking. Satisfactory matrices include inorganic oxides, including alumina, silica, naturally occurring and conventionally processed clays, such as bentonite, kaolin, sepiolite, attapulgite and halloysite. Such materials have few, if any, acid sites and therefore have little or no cracking activity.

Reaction conditions in the final reforming stage are specified to effectively utilize the particular performance advantages of the catalyst used in the stage. Thus, in the process of the invention, the reaction pressure of the final reforming stage is less than the pressure in the penultimate stage. Operating the final reforming stage at a lower pressure is made possible, at least in part, by the high catalytic stability of the medium pore molecular sieve catalyst of the present invention, which permits the catalyst to operate at lower pressures without significant fouling and premature activity failure. This in turn, permits the operation of the penultimate stage at relatively mild conditions, providing long catalyst life and high yields of hydrogen and desired high octane products.

The naphtha feed to the final stage is the intermediate reformate which is separated from the effluent of the penultimate stage. In the process, the intermediate reformate contacts the catalyst in the final stage at reforming reaction conditions, which reaction conditions include a temperature in the range from about 800° F. to about 1100° F., a pressure in the range from about 50 psig to about 250 psig and a feed rate in the range of from about 0.5 hr⁻¹ to about 5 hr⁻¹ LHSV. In some embodiments, the pressure in the reforming stage is less than 100 psig. Hydrogen may be added as an additional feed to the final reforming stage, but it is not required. In embodiments, hydrogen added with the feed is recovered from the process for separating the final stage effluent and is recycled to the final stage. The final stage is operated at conditions to maintain a molar H₂/hydrocarbon ratio in the range of 1:1 to 10:1. A molar H₂/hydrocarbon ratio in the range of 1:1 to 4:1 is exemplary.

Depending on the particular process, the effluent (otherwise termed the “final effluent”) from the final reforming stage may contain light (i.e. C₄− products and/or hydrogen) products which may be removed from the reformate in a final separation step prior to further processing for blending or use as a fuel. A hydrogen-rich stream may be separated from the effluent prior to the separation step, using, for example, a high pressure separator or other flash zone. C₄− hydrocarbons in the effluent may also be separated in a preliminary flash zone, either along with the hydrogen or in a subsequent flash zone. The reformate which is produced in the final reforming stage has an increased RON relative to that of the intermediate reformate which is the feed to the final reforming stage. In embodiments, the RON of the final reformate is at least 90 or at least 95, or at least 98. In some embodiments, the final reformate boils in the range from about 70° F. to about 280° F. In some such embodiments, the final reformate comprises at least 70 vol % C₅-C₈ hydrocarbons. In some embodiments, the final reformate boils in the range from about 100° F. to about 280° F. In some such embodiments, the final reformate comprises at least 70 vol % C₆-C₈ hydrocarbons. In some embodiments, the final reformate boils in the range from about 100° F. to about 230° F. In some such embodiments, the final reformate comprises at least 70 vol % C₆-C₇ hydrocarbons. In addition to the final reformate stream, a final light stream may also be recovered from the final effluent. In such cases, the final light stream boils in the range of about 70° to about 140° F. In some such embodiments, the final light stream comprises at least 70 vol % C₅ hydrocarbons.

The reformate is useful as a fuel or as a blend stock for a fuel. In some embodiments, at least a portion of the reformate from the final reforming stage is blended with at least a portion of the heavy reformate, which is recovered from the penultimate reforming stage; the blend may be used as a fuel or as a blend stock for a fuel.

Reference is now made to an embodiment of the invention illustrated in FIG. 1. A naphtha boiling range fraction 5 which boils within the range of 50° F. to 550° F. passes into the reaction stage 10 at a feed rate in the range of about 0.5 hr⁻¹ to about 5 hr⁻¹ LHSV. Reaction conditions in the reforming stage 10 include a temperature in the range from about 800° F. to about 1100° F. and a total pressure in the range of greater than 70 psig to about 400 psig.

The effluent 11 from the penultimate stage is an upgraded product, in that the RON has been increased during reaction in the penultimate stage 10. The penultimate stage effluent 11 comprises hydrocarbons and hydrogen generated during reaction in the penultimate stage and at least some of the hydrogen (if any) added to the feed upstream of the penultimate stage. In the embodiment illustrated in FIG. 1, the effluent is separated in separation zone 20 into a hydrogen-rich stream 21, a C₄-stream 22, an intermediate reformate 25 and a heavy reformate 26. In embodiments, this separation occurs in a single separation zone. In other embodiments, this separation is done in sequential zones, with the hydrogen, and optionally the C₄-stream, separated in one or more preliminary separation zones prior to the separation of the intermediate reformate 25 and the heavy reformate 26.

In the embodiment illustrated in FIG. 1, the intermediate reformate 25 comprises a substantial amount of the C₅-C₈ hydrocarbons contained in the effluent, with smaller quantities of C₄ and C₉ hydrocarbons. At least a portion of intermediate reformate 25 is passed to final reforming stage 30. Heavy reformate 26 contains a substantial amount of the C₉+ hydrocarbons contained in the effluent 11, and has an RON of greater than 98, preferably greater than 100.

Intermediate reformate 25 is passed to final reforming stage 30 for contact with a catalyst comprising platinum and at least one medium pore molecular sieve, at reaction conditions which include a temperature in the range from about 800° F. to about 1100° F. and a pressure in the range from about 50 psig to about 250 psig.

Effluent 31 from the final reforming stage is separated in separation zone 40, yielding at least a hydrogen-rich stream 41, a C₄− stream 42, and a final reformate stream 45. In embodiments, the final reformate stream boils in the C₅+ boiling range. As described above, this separation may take place in one, or multiple, separation zones, depending on the specific requirements of a particular process. In an embodiment, the final reformate stream 45 may be further combined with the heavy reformate 26 before further processing or use as a fuel or fuel blend stock. Hydrogen-rich stream 41 is combined with hydrogen-rich stream 21 before using in other refinery processes, and C₄− stream 42 is combined with C₄− stream 22.

Reference is now made to an embodiment of the invention illustrated in FIG. 2. A naphtha boiling range fraction 5 which boils within the range of 50 F.° to 550° F. passes into the reaction stage 10 at a feed rate in the range of about 0.5 hr⁻¹ to about 5 hr⁻¹ LHSV. Reaction conditions in the reforming stage 10 include a temperature in the range from about 800° F. to about 1100° F. and a total pressure in the range of greater than 70 psig to about 400 psig.

The effluent 11 from the penultimate stage is an upgraded product, in that the RON has been increased during reaction in the penultimate stage 10. The penultimate stage effluent 11 comprises hydrocarbons and hydrogen generated during reaction in the penultimate stage and at least some of the hydrogen (if any) added to the feed upstream of the penultimate stage. In the embodiment illustrated in FIG. 2, the effluent is separated in separation zone 20 into a hydrogen-rich stream 21, a C₄− stream 22, a light reformate 23, an intermediate reformate 24 and a heavy reformate 26. In embodiments, this separation occurs in a single separation zone. In other embodiments, this separation is done in sequential zones, with the hydrogen, and optionally the C₄− stream, separated in one or more preliminary separation zones prior to the separation of the light reformate 23, the intermediate reformate 24 and the heavy reformate 26.

In the embodiment illustrated in FIG. 2, the light reformate 23 comprises a substantial amount of the C₅ hydrocarbons contained in the effluent, with smaller quantities of C₄ and C₆ hydrocarbons. The intermediate stream comprises a substantial portion of the C₆-C₈ hydrocarbons contained in the effluent; the heavy reformate 26 contains a substantial amount of the C₉+ hydrocarbons contained in the effluent 11.

Intermediate reformate 24 is passed to final reforming stage 30 at a feed rate in the range of from about 0.5 hr⁻¹ to about 5 hr⁻¹ LHSV, for contact with a catalyst comprising platinum and at least one medium pore molecular sieve, at reaction conditions which include a temperature in the range from about 800° F. to about 1100° F. and a pressure in the range from about 50 psig to about 250 psig.

Effluent 31 from the final reforming stage is separated in separation zone 40, yielding at least a hydrogen-rich stream 41, a C₄− stream 42, a final C₅ stream 43 and a final reformate stream 44. In embodiments, the final reformate stream boils in the C₆+ boiling range. As described above, this separation may take place in one, or multiple, separation zones, depending on the specific requirements of a particular process. As shown in the embodiment illustrated in FIG. 2, the final reformate stream 44 is further combined with the heavy reformate 26 before further processing or use as a fuel or fuel blend stock, hydrogen-rich stream 41 is combined with hydrogen-rich stream 21 before using in other refinery processes, C₄− stream 42 is combined with C₄− stream 22 and final C₅ stream 43 is combined with C₅ stream 23.

The following examples are presented to exemplify embodiments of the invention but are not intended to limit the invention to the specific embodiments set forth. Unless indicated to the contrary, all parts and percentages are by weight. All numerical values are approximate. When numerical ranges are given, it should be understood that embodiments outside the stated ranges may still fall within the scope of the invention. Specific details described in each example should not be construed as necessary features of the invention.

EXAMPLES Example 1

A naphtha feed, with an API of 54.8, RON of 53.3 and an ASTM D-2887 simulated distillation shown in Table 1 was reformed in a penultimate stage using a commercial reforming catalyst comprising platinum with a rhenium promoter on an alumina support. Reaction conditions included a temperature of 840° F., a pressure of 200 psig, a 5:1 molar ratio of hydrogen to hydrocarbon ratio and a feed rate of 1.43 hr⁻¹ LHSV. The C₅+ liquid yield was 92.7 wt %. The hydrogen production was 975 standard cubic feet per barrel feed.

This C₅+ liquid product collected from the penultimate stage had an API of 46.6, an RON of 89 and an ASTM D-2887 simulated distillation as given in Table 2.

TABLE 1 ASTM D-2887 Simulated Distillation of the Feed to the Penultimate Stage Vol. % Temperature, ° F. IBP 182 10 199 30 227 50 258 70 291 90 336 EP 386

TABLE 2 ASTM D-2887 Simulated Distillation of the C₅+ Liquid Product Collected from the Penultimate Stage Vol. % Temperature, ° F. IBP 165 10 189 30 234 50 257 70 289 90 336 EP 411

Example 2

The C₅+ liquid product from Example 1 was distilled into an intermediate reformate and a heavy reformate. The intermediate reformate was found to represent 80 vol. % of the C₅+ liquid product from Example 1. The intermediate reformate, having an API of 55.7, an RON of 85 and an ASTM D-2887 simulated distillation as shown in Table 3, was used as feed to a final reforming stage in Example 3 and Comparative Example 1. The heavy reformate was found to represent 20 vol. % of the C₅+ liquid product from Example, 1. The heavy reformate had an API of 28.9 and an RON of 105, and is further described in Table 5.

TABLE 3 ASTM D-2887 Simulated Distillation of the Intermediate Reformate from the Penultimate Reforming Stage Vol. % Temperature, ° F. IBP 168 10 190 30 235 50 240 70 284 90 296 EP 336

Example 3

The intermediate reformate produced in Example 2 was used as feed to the final reforming stage which used a ZSM-5 zeolite based catalyst composited with 35% alumina binder material. The ZSM-5 had a SiO2/Al2O3 molar ratio of ˜2000 and was ion exchanged to the ammonium form before incorporating in a 65% zeolite/35% alumina extrudate. The extrudate was impregnated with 0.8% Pt, 0.3% Na, and 0.3% Mg by an incipient wetness procedure to make the final catalyst. The reaction conditions and experimental results are listed in Table 4.

TABLE 4 Comparison of the results from Example 3 and Comparative Example 1 Example 3 Comparative Example 1 Catalyst Pt/Na/Mg/ZSM-5 Pt/Re with alumina binder with alumina binder Temperature, ° F. 900 950 910 940 Pressure, psig 80 80 200 200 LHSV, hr⁻¹ 1.5 1.5 1.5 1.5 Molar H₂/hydrocarbon 2:1 2:1 5:1 5:1 Ratio RON of C₅+ 97.0 100.6 96.9 101.8 C₅+ Yield, wt % 92.7 88.4 88.9 85.2 H₂ Yield, scf/bbl feed 300 430 130 175

Comparative Example 1

The intermediate reformate produced in Example 2 was contacted with a commercial platinum/rhenium on alumina based catalyst described in Example 1 in a final reforming stage. The reaction conditions and experimental results are listed in Table 4 and compared with the results from Example 3 which uses a ZSM-5 zeolite based catalyst.

Example 3 and Comparative Example 1 show the benefit of ZSM-5 zeolite based catalysts when compared with commercial platinum on alumina catalysts in terms of C₅+ yield and hydrogen production at similar C₅+ RON.

Example 4

A product which was produced in the final stage reforming of the intermediate reformate in Example 3 was blended with the heavy reformate (Example 2) which was not subjected to the final stage reforming. The total RON of C₅+, total C₅+ yield and total H₂ production of the blended final product are given in Table 5 based on using the total C₅+ penultimate effluent as feed (which is distilled into intermediate reformate and heavy reformate in Example 2). The results are compared to those obtained from Comparative Example 2 where the total C₅+ product was produced from the total C₅+ penultimate effluent as feed, without distillation into an intermediate and heavy reformate.

Comparative Example 2

The total C₅+ product produced in Example 1, without distillation into an intermediate and heavy reformate, was contacted with a ZSM-5 zeolite based catalyst described in Example 3 in a final reforming stage at 930° F., 80 psig, 2:1 molar ratio of hydrogen to hydrocarbon and 1.5 hr⁻¹ LHSV feed rate. The C₅+ liquid yield was 89.9 wt. % and RON of the C₅+ liquid product from the final reforming stage was 97.4. The hydrogen production was 190 standard cubic feet per barrel feed. In Table 5, the results from Example 4, where the final product was is a blend from (i) the product produced in the final stage reforming of the intermediate reformate in Example 3 and (ii) the heavy reformate (Example 2) which was not subjected to the final stage reforming, are compared to those obtained from Comparative Example 2, where the total C₅+ product was produced from the total C₅+ penultimate effluent as feed, without distillation into an intermediate and heavy reformate.

TABLE 5 Comparison of results from Example 4 and Comparative Example 2 Example 4 Comparative Example 3 Example 2 Example 2 Feedstock Intermediate Heavy reformate Total C₅+ reformate (Ex. 2, Table 3) penultimate effluent (Ex. 2, Table 3) (Ex. 1, Table 2) Catalyst Pt/Na/Mg/ZSM-5 Not subjected to Pt/Na/Mg/ZSM-5 with alumina the final stage with alumina binder binder reforming Temperature, ° F. 900 — 930 Pressure, psig  80 —  80 LHSV, hr⁻¹  1.5 —  1.5 Molar H₂/hydrocarbon 2:1 — 2:1 Ratio RON of C₅+  97.0⁽¹⁾ 105⁽²⁾  97.4⁽³⁾ C₅+ Yield, wt %  92.7⁽¹⁾ 100⁽²⁾  89.9⁽³⁾ H₂ Yield, scf/bbl feed 300⁽¹⁾ — 190⁽³⁾ Total RON of C₅+ 98.7⁽⁴⁾  97.4⁽³⁾ Total C₅+ Yield, wt % 94.2⁽⁴⁾  89.9⁽³⁾ Total H₂ Yield, scf/bbl feed 240⁽⁴⁾   190⁽³⁾ Notes to Table 5: ⁽¹⁾For Example 3: RON of C₅+, C₅+ yield and H₂ production of the product are given based on the intermediate reformate as feed. ⁽²⁾For Example 2: RON of C₅+ and C₅+ yield are given based on the heavy reformate which is not subjected to the final stage reforming. ⁽³⁾For Comparative Example 2: RON of C₅+, C₅+ yield and H₂ production of the product are given based on the total C₅+ penultimate effluent as feed. ⁽⁴⁾For Example 4: Total RON of C₅+, total C₅+ yield and total H₂ production are given based on the total C₅+ penultimate effluent as feed (which is distilled into intermediate reformate and heavy reformate in Example 2). The final product of Example 4 consists of a blend of (i) the product from the final stage reforming of the intermediate reformate and (ii) the heavy reformate which is not subjected to the final stage reforming.

Example 4 and Comparative Example 2 show the benefit of the intermediate reformate as feed to the final reforming stage when compared with using the full boiling range C₅+ feed, with the ZSM-5 zeolite based catalyst, in terms of C₅+ yield, hydrogen production and C₅+ RON.

The RON values reported in Examples 3-4 and Comparative Examples 1 and 2 above are calculated values, based on RON blending correlations applied to a composition analysis using gas chromatography. The method was calibrated to achieve a difference between measured and calculated RON's of within ±0.8. 

1. A reforming process comprising: a. contacting a naphtha boiling range feedstock in a penultimate stage of a multi-stage reforming process at a first reforming pressure to produce a penultimate effluent; b. separating at least a portion of the penultimate effluent into at least an intermediate reformate and a heavy reformate, wherein the intermediate reformate has a mid-boiling point that is lower than that of the heavy reformate; and c. contacting at least a portion of the intermediate reformate in a final stage of the multi-stage reforming process at a second reforming pressure with a catalyst comprising at least one medium pore molecular sieve to produce a final effluent comprising a final reformate, wherein the first reforming pressure is greater than the second reforming pressure.
 2. The process of claim 1, wherein the naphtha boiling range feedstock boils in the range from about 50° F. to about 550° F.
 3. The process of claim 1, wherein the intermediate reformate comprises at least 70 vol % C₅-C₈ hydrocarbons.
 4. The process of claim 3, wherein the intermediate reformate comprises at least 70 vol % C₆-C₈ hydrocarbons.
 5. The process of claim 1, wherein the heavy reformate comprises at least 70 vol % C₉+ hydrocarbons.
 6. The process of claim 1, wherein the RON of the intermediate reformate is higher than the RON of the naphtha boiling range feedstock.
 7. The process of claim 1, wherein the intermediate reformate has an RON within the range of 65 to less than
 100. 8. The process of claim 1, wherein the heavy reformate has an RON of at least
 95. 9. The process of claim 1, wherein at least 70 vol % of the final reformate boils in the range of about 70° F. or higher.
 10. The process of claim 1, wherein the final reformate has an RON of 90 or greater.
 11. The process of claim 10, wherein the final reformate has an RON which is greater than the RON of the intermediate reformate.
 12. The process of claim 1, wherein the second reforming pressure, of the final reforming stage, is within the range of 50 psig to 250 psig.
 13. The process of claim 12, wherein the second reforming pressure, of the final reforming stage, is within the range of 50 psig to 150 psig.
 14. The process of claim 1, wherein the first reforming pressure, of the penultimate reforming stage, is within the range of 70 psig to 400 psig.
 15. The process of claim 1, wherein the first reforming pressure is within the range of 200 psig to 400 psig and within the second reforming pressure is within the range of 50 psig to 150 psig.
 16. The process of claim 1, wherein the catalyst within the penultimate stage comprises a Group VIII metal and a prompter supported on a porous refractory inorganic oxide support.
 17. The process of claim 15, wherein the Group VIII metal is platinum.
 18. The process of claim 15 wherein the catalyst comprises platinum and rhenium on an alumina support.
 19. The process of claim 1, wherein the medium pore molecular sieve is selected from the group consisting of ZSM-5, ZSM-11, ZSM-12, ZSM-22, ZSM-23, ZSM-35, ZSM-38, ZSM-48 MCM-22, SSZ-20, SSZ-25, SSZ-32, SSZ-35, SSZ-37, SSZ-44, SSZ-45, SSZ-47, SSZ-57, SSZ-58, SSZ-74, SUZ-4, EU-1, NU-85, NU-87, NU-88, IM-5, TNU-9, ESR-10, TNU-10 and combinations thereof.
 20. The process of claim 1, wherein the medium pore molecular sieve comprises ZSM-5 having a silica to alumina molar ratio of at least 200:1.
 21. The process of claim 1, wherein the medium pore molecular sieve comprises ZSM-5 having a silica to alumina molar ratio of at least 500:1.
 22. The process of claim 1, wherein the medium pore molecular sieve comprises ZSM-5 having less than 5,000 ppm alkali.
 23. The process of claim 1, wherein the catalyst in the final reforming stage further comprises a Group VIII metal selected from platinum or palladium.
 24. The process of claim 1, further comprising blending the heavy reformate with the final reformate to produce a fuel or a fuel blend stock.
 25. A reforming process comprising: a. contacting a naphtha boiling range feedstock in a penultimate stage of a multi-stage reforming process at a first reforming pressure to produce an penultimate effluent; b. separating at least a portion of the penultimate effluent into at least a light reformate, an intermediate reformate and a heavy reformate, wherein the light reformate has a mid-boiling point that is lower than that of the intermediate reformate, and wherein the intermediate reformate has a mid-boiling point that is lower than that of the heavy reformate; and c. contacting at least a portion of the intermediate reformate in a final stage of the multi-stage reforming process at a second reforming pressure with a catalyst comprising at least one medium pore molecular sieve to produce an final effluent comprising a final reformate, wherein the first reforming pressure is greater than the second reforming pressure.
 26. The process of claim 24, wherein the light reformate comprises at least 70 vol % C₅ hydrocarbons.
 27. The process of claim 24, wherein the intermediate reformate comprises at least 70 vol % C₅-C₈ hydrocarbons.
 28. The process of Claim 26, wherein the intermediate reformate comprises at least 70 vol % C₆-C₈ hydrocarbons.
 29. The process of claim 24, wherein the RON of the intermediate reformate is higher than the RON of the naphtha boiling range feedstock.
 30. The process of claim 24, wherein the intermediate reformate has ah RON of at least
 65. 31. The process of claim 24, wherein the heavy reformate has an RON of 95 or greater.
 32. The process of claim 24, wherein the final reformate has an RON of 90 or greater.
 33. The process of claim 24, wherein the final reformate has an RON which is greater than the RON of the intermediate reformate.
 34. The process of claim 24, further comprising: a. separating the final effluent into at least a final C₅ stream and a final reformate stream; b. combining the final C₅ stream with the light reformate stream; and c. combining the final reformate with the heavy reformate.
 35. The process of claim 33, wherein the final reformate stream comprises at least 70 vol % C₅+ hydrocarbons.
 36. The process of claim 33, wherein the final reformate stream comprises at least 70 vol % C₆+ hydrocarbons.
 37. The process of claim 33, wherein the final reformate stream comprises at least 70 vol % C₅₋C₈ hydrocarbons. 